Yi-feng Yang

The surface of the uranium compound UTe2 crystal looks like a frozen sea: in some places, electrons move freely; in others, they get stuck near atoms. A scanning tunneling microscope, a device that probes the surface with an atomically sharp tip and senses individual electrons, revealed that this landscape is not random.

The uranium-arsenic crystal UAs2 under pressure behaves like a house with two rooms. In one room, electrons sit still; in the other, they roam freely. Under normal conditions, it's a classic "lattice Kondo" system: heavy, almost immobile electrons on 5f5/2 orbitals are surrounded by a sea of fast conduction electrons.